Clinical Report: Shifts in Endemic Respiratory Virus Circulation During COVID-19 Pandemic
Overview
The COVID-19 pandemic and associated public health measures caused significant disruptions in the circulation patterns of endemic respiratory viruses. Winter-dominant viruses like influenza A and RSV experienced marked declines and delayed recovery, whereas spring and year-round viruses such as human metapneumovirus and adenovirus showed quicker normalization.
Background
Respiratory viruses typically follow predictable seasonal patterns influenced by environmental and host factors. In temperate North America, viruses cluster into winter, spring, and year-round circulation groups. The emergence of SARS-CoV-2 in early 2020 and subsequent mitigation strategies led to historically low levels of many endemic respiratory viruses. Previous pandemics caused transient disruptions, but SARS-CoV-2 induced prolonged and variable alterations in virus circulation.
Data Highlights
Virus Group
Seasonality
Post-SARS-CoV-2 Positivity Change
Recovery Time
Seasonal Pattern Shift
Influenza A, RSV
Winter
Significant decline
Protracted resurgence
Altered seasonality; influenza A semiannual pattern until 2024
Human metapneumovirus, Parainfluenza 3
Spring
Minimal disruption
Normalized within 2 seasons
Median peak displacement normalized quickly
Adenovirus, Rhinovirus/Enterovirus
Year-round
Minimal disruption
Rapid normalization
No significant seasonal shift
Key Findings
Winter viruses (influenza A, RSV) showed significant declines in positivity and experienced delayed recovery with altered seasonal timing.
Spring viruses (human metapneumovirus, parainfluenza 3) and year-round viruses (adenovirus, rhinovirus/enterovirus) were resilient, quickly returning to prepandemic positivity levels.
Influenza A shifted to a semiannual circulation pattern before returning to normal seasonality by 2024.
Median peak displacement for spring viruses normalized within two seasons post-pandemic onset.
The degree of disruption correlated with the overlap of virus circulation peaks and SARS-CoV-2 peaks.
Public health countermeasures disproportionately affected viruses with wintertime circulation overlapping SARS-CoV-2 peaks.
Clinical Implications
Clinicians should anticipate potential shifts in respiratory virus seasonality and delayed resurgence of winter viruses following pandemics like COVID-19. Surveillance systems must adapt to altered timing and intensity of virus circulation to optimize diagnosis, prevention, and resource allocation. Understanding virus-specific recovery patterns can inform targeted public health interventions during and after pandemics.
Conclusion
The COVID-19 pandemic caused uneven disruptions in endemic respiratory virus circulation, with winter-dominant viruses experiencing prolonged alterations while spring and year-round viruses recovered more rapidly. These findings highlight the importance of considering virus seasonality and circulation overlap in pandemic preparedness and response.
References
Sullivan et al. 2024 -- Shifts in the Circulation and Testing of Endemic Respiratory Viruses Before, During, and After the COVID-19 Pandemic
